Permanent magnet retaining arrangement for high speed rotors

ABSTRACT

In the embodiments described in the specification, permanent magnets are retained on a permanent magnet rotor rim by inverted U-shaped retainers and in one embodiment the outer surfaces of the retainers converge inwardly in the radially outward direction and engage corresponding surfaces of adjacent pole pieces which converge inwardly in the radially outward direction. In another embodiment the U-shaped retainers are affixed to the rotor rim by screws accessible through openings in the radially outer wall of the retainers and a further embodiment each retainer has outwardly projecting flanges which are affixed to the rotor rim by screws.

BACKGROUND OF THE INVENTION

[0001] This invention relates to arrangements for retaining permanentmagnets radially in position in permanent magnet rotors for electricmachines operating at high speed.

[0002] Conventional arrangements for retaining magnets in position inrotors for electric machines include slot wedges which span the distancebetween adjacent pole pieces across the radially outer surface of themagnets. Such arrangements have limited centrifugal load carryingcapability.

[0003] The Burson U.S. Pat. No. 4,179,634 discloses a magneto rotorhaving permanent magnets which are retained in a cavity formed in therotor by pole pieces disposed on opposite sides of the magnet andretained by retaining pins received in axially extending slots in thepole pieces.

[0004] The U.S. Pat. No. 2,516,901 to Morill discloses a permanentmagnet rotor having a hub to which permanent magnets are affixed byscrews engaging shoulders on the magnets. In addition, rings may be castaround the shoulders of the magnets and the screws to assist inretaining the magnets on the hub.

[0005] In the magneto shown in the Iwata et al. U.S. Pat. No. 5,811,908,U-shaped permanent magnet retention channels made of magnetic materialhave projections at the outer ends of the walls which are received incorresponding grooves in adjacent pole pieces.

[0006] According to the Tomite et al. U.S. Pat. No. 4,745,319, permanentmagnets are secured to the inner surface of a surrounding yoke byattaching one surface of a U-shaped elastic retainer member to the innersurface of the yoke and attaching the ends of the U-shaped retainer toedges of adjacent magnets which are to be retained in the yoke.

SUMMARY OF THE INVENTION

[0007] Accordingly, it is an object of the present invention to providea retaining arrangement for permanent magnets in a rotor for an electricmachine which overcomes disadvantages of the prior art.

[0008] Another object of the invention is to provide a retainingarrangement for permanent magnets by which they are secured effectivelyin the radial direction during high speed operation of a rotor.

[0009] These and other objects of the invention are attained byproviding a retaining arrangement in which permanent magnets areretained in a permanent magnet rotor by U-shaped retainers supportedfrom a rotor rim, the retainers being made of nonmagnetic material andhaving a smooth channel to receive magnets and provide radial support.In one embodiment the U-shaped retainers have laterally outer surfaceswhich converge inwardly in the radially outward direction and theadjacent opposed pole pieces, which are affixed to the rotor rim, havecorresponding lateral surfaces which converge inwardly in the radiallyoutward direction. In another embodiment, the U-shaped retainer isconnected to the rotor rim by fasteners such as screws.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Further objects and advantages of the invention will be apparentfrom a reading of the following description in conjunction with theaccompanying drawings in which:

[0011]FIG. 1 is a schematic perspective view illustrating arepresentative embodiment of a permanent magnet rotor for an electricmachine having a magnet retaining arrangement in accordance with theinvention;

[0012]FIG. 2 is an enlarged fragmentary view of the magnet retainingarrangement shown in FIG. 1.;

[0013]FIG. 3 is a cross sectional view showing the shape of the magnetretainer used in the arrangement shown in FIGS. 1 and 2;

[0014]FIG. 4 is a fragmentary cross sectional view illustrating apermanent magnet rotor having an alternative magnet retainingarrangement in accordance with the invention; and

[0015]FIG. 5 is a fragmentary cross sectional view showing a permanentmagnet rotor having still another embodiment of a magnet retainingarrangement in accordance with the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0016] In the representative embodiment of the invention illustrated inFIGS. 1-3, a rotor 10 has a shaft 12 connected to an outer rim 14 by anarray of angularly spaced inclined blades 16 forming a rim-drivenpropeller which may be used, for example, in a propulsion pod. A spacedcircumferential array of pole pieces 18, made of laminated magneticmaterial in the conventional manner is mechanically attached to the rimby key members 20 held by screws 22.

[0017] Between each adjacent pair of pole pieces 18 a magnet 24 is heldin position by a slot wedge 26 made of nonmagnetic material and havinggrooves 28 in its opposite edges to receive projections 30 of theadjacent pole pieces 18.

[0018] In order to facilitate radial retention of the magnets 24 duringhigh speed rotation of the rotor 10, an inverted U-shaped retainer 32,also made of nonmagnetic material, is located in the space between eachmagnet 24 and the adjacent surfaces of the pole pieces 18 and the slotwedge 26. As best seen in FIG. 3, the U-shaped retainer 32 hasrectangularly arranged inner surfaces 34 and 36 to conform to therectangular periphery of the magnet 24 and is formed with a radiallyouter surface 38 which engages the radially inner surface 40 of theadjacent slot wedge 26 and with circumferentially outer surfaces 44which converge inwardly in the radially outward direction to conform tocorresponding inwardly converging surfaces 46 of the adjacent polepieces 18 to facilitate retention of the U-shaped retainer 32 and themagnet 24 enclosed therein during high speed rotation of the rotor 10.

[0019] In addition, a circumferential outer wrap 50 of fiber-reinforcedpolymer material surrounds the entire peripheral surface of the entirerotor structure. With this arrangement, the magnet retention isfacilitated by the engaging angled surfaces 44 and 46 of the U-shapedretainer and the pole pieces as well as the fiber-reinforced polymerwrap 50.

[0020] In the alternative embodiment illustrated in the fragmentary viewof FIG. 4, a rotor 60 has an outer rim 62 to which nonmagnetic U-shapedmagnet retainers 66 are affixed by screws 68 accessible through holes 70formed in the top wall 72 of the retainers. Permanent magnets 76 areinserted longitudinally into the channels formed in the U-shapedretainers. Pole pieces 80 between each adjacent pair of magnet retainers66 are secured to the rim 62 by opposed jaws 82 projecting from the rim62 to receive a correspondingly shaped portion 84 of the pole piece 80which may be retained securely in position by a bolt 86 extendingthrough the jaws and the portion 84.

[0021] In the further embodiment schematically shown in FIG. 5, a rotor90 has a peripheral rim 94 to which pole pieces 96 are secured byopposed jaws 98 and a bolt 100 in the manner described with respect toFIG. 4. In this case, nonmagnetic U-shaped magnet retainers 104 haveangularly projecting flanges 106 which are fastened to correspondingsurfaces 108 of the rim 94 by screws 110 before the pole pieces aremounted on the rim. The U-shaped retainers have access openings 112through which the bolts 100 can be inserted to retain the pole piecesafter the retainers 104 have been secured to the rim 94. Thereafter,permanent magnets 116 are inserted into channels 118 formed by theretainers 104. With this arrangement, the magnets 116 and theirretainers 104 are securely held in position during high speed rotationby the screws 110 as well as by the pole pieces 96 and their retainingbolts 100. The outer surface of the rotor may be enclosed by afiber-reinforced polymer wrap 120 as in the other embodiments.

[0022] Although the invention has been described herein with referenceto specific embodiments, many modifications and variations therein willreadily occur to those skilled in the art. Accordingly, all suchvariations and modifications are included within the intended scope ofthe invention.

We claim:
 1. A permanent magnet rotor arrangement comprising: a rotorhaving a rim; a circumferential array of pole pieces made of magneticmaterial affixed to the rotor rim; an inverted U-shaped magnet retainermade of nonmagnetic material and formed with a channel mounted betweeneach adjacent pair of pole pieces; and at least one permanent magnetinserted into the channel formed in each U-shaped retainer.
 2. Apermanent magnet rotor arrangement according to claim 1 wherein eachadjacent pair of pole pieces has surfaces facing the U-shaped magnetretainer which converge inwardly in the radially outward direction andthe U-shaped retainer has corresponding outer surfaces which convergeinwardly in the radially outward direction and engage the inwardlyconverging surfaces of the pole pieces.
 3. A permanent magnet rotorarrangement according to claim 1 wherein the U-shaped permanent magnetretainer is affixed to the rotor rim by a mechanical attachment.
 4. Apermanent magnet rotor arrangement according to claim 3 wherein themechanical attachment comprises screws.
 5. A permanent magnet rotorarrangement according to claim 4 wherein the U-shaped magnet retainerhas projecting flanges engaging a rim portion and the adjacent polepieces extend in the angular direction over the projecting flanges.
 6. Apermanent magnet rotor arrangement according to claim 1 including anouter wrap of fiber-reinforced polymer material surrounding the rotor.7. A permanent magnet rotor arrangement according to claim 1 wherein thepole pieces are mechanically connected to corresponding rim portions bybolts.